Even harmonic resonance - an unusual problem

The paper is a case study examining the cause, effect and solution of an actual "noncharacteristic" even harmonic problem in an electrochemical plant. While issues concerning "characteristic" harmonics are well documented in the literature, limited information is available describing how noncharacteristic harmonic currents create operational problems. The author has not found any papers describing a case of even harmonic resonance and would like to share the experience of resolving a 4^th harmonic resonance problem in the hopes it will benefit others.